256 THE DEVONIAN FOSSILS OF CANADA WEST. 
Fig. 63. Fig. 64. 
This only differs from S. mucronata in the larger area of the ven- 
tral valve, as shewn in Fig. 60, and from S. dimeszalis by the absence 
of the median rib in the sinus, and no groove on the mesial fold. 
I do not pretend to decide that the above all belong to one species, 
or that they should be all referred to S. varicosa. There are numerous 
species of brachiopoda described by Prof. Hall and others, without 
figures or measurements, which never can be recognized or identified 
except by the persons who have the original specimens in their 
possession. 
SPIRIFERA DUODENARIA-—( Hall.) 
DELTHYRIS DUODENARIA.—Hall. Geology of the 4th District of 
New York, p.17. Fig. 5. 1848. 
Fig. 67. 
Fig. 65. SPIRIFERA DUODENARIA.—(Hall.) Dorsal view of a large specimen. 
Fig. 66. Shews the narrow area and the close approximation of the beaks. 
Fig. 67. Dorsal view. 
Description.—This species is distinguished by its smooth rounded 
ribs. The form is sub-semicircular or sub-triangular ; the hinge-line 
straight extended, equal to the greatest width of the shell; both 
valves moderately convex; the dorsal valve usually flattened or 
concave near the cardinal extremity; the areas very narrow; beaks 
small, short, pointed, incuryed, nearly in contact with each other. 
From twelve to fourteen strong rounded ribs, gradually decreasing in 
